Low thermal expansion steel and method for manufacturing same

Abstract

A low thermal expansion steel according to an embodiment of the present invention comprises, in weight %, C: 0.000% (exclusive) to 0.040% (inclusive), Si: 0.080% to 0.200% (both inclusive), Mn: 0.150% to 0.450% (both inclusive), P: 0.000% (exclusive) to 0.0030% (inclusive), S: 0.0000% (exclusive) to 0.0030% (inclusive), Cr: 0.00% (exclusive) to 2.00% (inclusive), Ni: 34.0% to 39.0% (both inclusive), Co: 0.000% (exclusive) to 0.400% (inclusive), with the balance being Fe and inevitable impurities, and satisfies the value of formula (1) 0.5×[Cr] − [Ni] − 2.7×[Mn] − 4×[Co] + 40 ranging from 0.00 to 4.00 (both inclusive).

Description

Low thermal expansion steel and method of manufacturing the same

[0001] The present invention relates to a low thermal expansion steel with minimal cracking due to temperature changes and a method for manufacturing the same.

[0002] With the recent increase in demand for the transportation and storage of liquefied natural gas, the demand for container materials capable of storing liquids at cryogenic temperatures is rising significantly.

[0003] Generally, since materials undergo changes in length with temperature, deformation resulting from these length changes can occur in storage container materials in cryogenic environments. Thermal expansion caused by temperature fluctuations can generate stress within the material, which can lead to the formation of cracks and potentially result in major accidents.

[0004] To prevent material damage, there is a need to develop materials with low coefficients of thermal expansion at room and cryogenic temperatures that exhibit minimal length change due to temperature variations.

[0005] To solve the aforementioned problems, the present invention aims to provide a low thermal expansion steel with excellent crack resistance at room temperature and cryogenic temperatures and a method for manufacturing the same by optimizing alloy composition and controlling the compositional relationship.

[0006] The problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by those skilled in the art from the description below.

[0007] As a means to achieve the above-mentioned purpose, a low thermal expansion steel according to one embodiment of the present invention may be a low thermal expansion steel comprising, in weight %, C: greater than 0.000% and less than or equal to 0.040%, Si: greater than 0.080% and less than or equal to 0.200%, Mn: greater than 0.150% and less than or equal to 0.450%, P: greater than 0.000% and less than or equal to 0.0030%, S: greater than 0.0000% and less than or equal to 0.0030%, Cr: greater than 0.00% and less than or equal to 2.00%, Ni: greater than 34.0% and less than or equal to 39.0%, Co: greater than 0.000% and less than or equal to 0.400%, and the remainder being Fe and unavoidable impurities, wherein the value of the following formula (1) is greater than or equal to 0.00 and less than or equal to 4.00.

[0008] Equation (1): 0.5*[Cr] - [Ni] - 2.7*[Mn] - 4*[Co] + 40

[0009] (In Equation (1), [Cr], [Ni], [Mn] and [Co] represent the content (weight%) of each element.)

[0010] A low thermal expansion steel according to one embodiment of the present invention may be a low thermal expansion steel in which the value of the following formula (2) is 0.00 or less.

[0011] Equation (2): 175*[C] + 11[Si] + 3*[Mn] + 3*[Cr] - 8

[0012] (In Equation (2), [C], [Si], [Mn], and [Cr] represent the content (weight%) of each element.)

[0013] A low thermal expansion steel according to one embodiment of the present invention has a coefficient of thermal expansion of 3.00 x 10⁻⁶ from room temperature to 100°C. -6 It may be a low thermal expansion steel with a temperature of / ℃ or lower.

[0014] A low thermal expansion steel according to one embodiment of the present invention has a coefficient of thermal expansion of 3.00 x 10 from -180°C to 0°C. -6 It may be a low thermal expansion steel with a temperature of / ℃ or lower.

[0015] A low thermal expansion steel according to one embodiment of the present invention may be a low thermal expansion steel having a hardness of 200 Hv or less.

[0016] A method for manufacturing low thermal expansion steel according to one embodiment of the present invention comprises the steps of: manufacturing a steel material having, in weight %, C: greater than 0.000% and less than or equal to 0.040%, Si: greater than 0.080% and less than or equal to 0.200%, Mn: greater than 0.150% and less than or equal to 0.450%, P: greater than 0.000% and less than or equal to 0.0030%, S: greater than 0.0000% and less than or equal to 0.0030%, Cr: greater than 0.00% and less than or equal to 2.00%, Ni: greater than 34.0% and less than or equal to 39.0%, Co: greater than 0.000% and less than or equal to 0.400%, and the remainder being Fe and unavoidable impurities, wherein the value of the following formula (1) is 0.00 and less than or equal to 4.00; and reheating the steel material at 1150℃ to 1300℃ and hot rolling it. The method for manufacturing low thermal expansion steel may include the step of hot rolling annealing the above hot-rolled material at 800°C to 1000°C.

[0017] Equation (1): 0.5*[Cr] - [Ni] - 2.7*[Mn] - 4*[Co] + 40

[0018] (In Equation (1), [Cr], [Ni], [Mn] and [Co] represent the content (weight%) of each element.)

[0019] In a method for manufacturing low thermal expansion steel according to one embodiment of the present invention, the steel material may be a method for manufacturing low thermal expansion steel in which the value of the following formula (2) is 0.00 or less.

[0020] Equation (2): 175*[C] + 11[Si] + 3*[Mn] + 3*[Cr] - 8

[0021] (In Equation (2), [C], [Si], [Mn], and [Cr] represent the content (weight%) of each element.)

[0022] A method for manufacturing low thermal expansion steel according to one embodiment of the present invention may further include the step of cold rolling the hot-rolled steel sheet with a reduction rate of 50% or more and cold rolling annealing at 800°C to 950°C to manufacture a cold-rolled steel sheet.

[0023] According to an embodiment of the present invention, a low thermal expansion steel with excellent crack resistance at room temperature and cryogenic temperature and a method for manufacturing the same can be provided.

[0024] The effects obtainable from this invention are not limited to those mentioned above, and other unmentioned effects will be clearly understood by those skilled in the art to which this invention pertains from the description below.

[0025] Preferred embodiments of the present invention are described below. However, embodiments of the present invention may be modified in various other forms, and the technical concept of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more completely explain the present invention to those with average knowledge in the relevant technical field.

[0026] The terms used in this application are used merely to describe specific examples. For this reason, singular expressions include plural expressions unless the context clearly requires them to be singular. Additionally, it should be noted that terms such as “comprising” or “comprising” used in this application are used to clearly indicate the presence of features, steps, functions, components, or combinations thereof described in the specification, and are not used to preliminarily exclude the existence of other features, steps, functions, components, or combinations thereof.

[0027] Meanwhile, unless otherwise defined, all terms used in this specification shall be understood to have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Accordingly, unless explicitly defined in this specification, specific terms should not be interpreted in an overly ideal or formal sense.

[0028] Additionally, terms such as "about," "substantially," etc., in this specification are used to mean at or near the stated value when inherent manufacturing and material tolerances are presented in the said sense, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosed content in which precise or absolute values ​​are mentioned to aid in understanding the invention.

[0029] Unless otherwise specifically stated in this specification, the % indicating the content of each element is based on weight.

[0030] A low thermal expansion steel according to one embodiment may comprise, in weight %, C: greater than 0.000% and less than or equal to 0.040%, Si: greater than 0.080% and less than or equal to 0.200%, Mn: greater than 0.150% and less than or equal to 0.450%, P: greater than 0.000% and less than or equal to 0.0030%, S: greater than 0.0000% and less than or equal to 0.0030%, Cr: greater than 0.00% and less than or equal to 2.00%, Ni: greater than 34.0% and less than or equal to 39.0%, Co: greater than 0.000% and less than or equal to 0.400%, and the remainder being Fe and unavoidable impurities.

[0031] Hereinafter, the reason for the numerical limitation of the alloy component content in the embodiments of the present invention will be explained.

[0032] C (carbon) may be greater than 0.000% and less than or equal to 0.040%.

[0033] C is an element that degrades thermal expansion through the formation of carbides. Therefore, the C content must be managed to a very low level through various decarburization processes. However, since such ultra-low decarburization processes can increase costs, it is important to set an appropriate carbon content. Meanwhile, increasing the C content exhibits an effect of increasing strength, which offers advantages as it allows for use as a thin sheet material. In the present invention, thermal expansion characteristics were evaluated across various C content ranges, and it was confirmed that low thermal expansion characteristics are maintained without influence from the C content at a content of 0.040% or less. Therefore, in the present invention, the C content may be limited to greater than 0.000% and less than or equal to 0.040%. Preferably, the C content may be greater than 0.008% and less than or equal to 0.031%.

[0034] Si (silicon) may be 0.080% or more and 0.200% or less.

[0035] Si is an essential element added for deoxidation during the refining of alloys. An increase in Si content facilitates deoxidation during refining, which is advantageous for reducing O content and controlling inclusions. However, since the addition of Si increases thermal expansion, it is necessary to reduce it to suppress the increase in the coefficient of thermal expansion. Therefore, in the present invention, the Si content may be limited to 0.080% or more and 0.200% or less. Preferably, the Si content may be 0.080% or more and 0.180% or less.

[0036] Mn (manganese) may be 0.150% or more and 0.450% or less.

[0037] Manganese is useful as a solid solution strengthening element and is also effective in improving hot workability. In particular, since it is used as a deoxidizer along with Si during alloy refining, its addition is an essential element. However, to ensure low thermal expansion for materials used in liquefied natural gas (LNG) storage containers, it is necessary to limit the addition of large amounts. In this invention, by adding Mn up to a level of 0.400% and adjusting the Cr, Ni, and Co components, a 3.00 x 10⁻³ material applicable as a material for LNG storage containers is obtained.-6 A coefficient of thermal expansion of / ℃ or less was secured. It was confirmed that there is no change in the coefficient of thermal expansion according to the Mn content when Mn is added at 0.450% or less. Therefore, in the present invention, the Mn content may be 0.150% or more and 0.450% or less. Preferably, the Mn content may be 0.190% or more and 0.430% or less.

[0038] P(phosphorus) may be greater than 0.0000% and less than or equal to 0.0030%.

[0039] P is an impurity inevitably contained in steel and is a major cause of intergranular corrosion or impaired hot workability; therefore, it is desirable to control its content to be as low as possible. However, excessive reduction leads to increased refining costs, so it is necessary to manage it below an appropriate level. In the present invention, the P content may be limited to greater than 0.0000% and less than or equal to 0.0030%. Preferably, the P content may be greater than or equal to 0.0010% and less than or equal to 0.0018%.

[0040] S (sulfur) may be greater than 0.0000% and less than or equal to 0.0030%.

[0041] S is an impurity inevitably contained in steel and is an element that causes segregation at grain boundaries, which is a major cause of impediment to hot workability. In particular, since it can cause shape defects or cracks during welding, it is desirable to control its content to be as low as possible. In the present invention, the S content may be limited to greater than 0.0000% and less than or equal to 0.0030%. Preferably, the S content may be greater than or equal to 0.0004% and less than or equal to 0.0020%.

[0042] Cr (chromium) may be greater than 0.00% and less than or equal to 2.00%.

[0043] Cr is an essential element in the stainless steel manufacturing process. Therefore, when manufacturing other steel grades in the usual stainless steel process, Cr is introduced from materials such as molten metal, making it difficult to remove. The addition of Cr is effective in improving mechanical properties such as impact toughness. However, since Cr is an element that increases the coefficient of thermal expansion, it is desirable to control its content to be as low as possible in low thermal expansion steels. In the present invention, by controlling the Ni content, which reduces thermal expansion, a component range was derived in which the Cr content can be added up to a maximum of 2.00%. In the present invention, the Cr content can be limited to greater than 0.00% and less than or equal to 2.00%. Preferably, the Cr content can be greater than 0.03% and less than or equal to 1.02%.

[0044] Ni (nickel) may be 34.0% or more and 39.0% or less.

[0045] Ni is an essential element for achieving low thermal expansion. Ni contributes to lowering the coefficient of thermal expansion of low thermal expansion steel and plays a role in stabilizing austenite. In the present invention, the Ni content can be limited to 34.0% or more and 39.0% or less. Preferably, the Ni content may be 34.1% or more and 39.0% or less. By adjusting components such as Cr, Mn, and Co within this range, 3.00 x 10⁻³ is applicable as a material for liquefied natural gas storage containers. -6 A coefficient of thermal expansion of / ℃ or less was secured.

[0046] Co (cobalt) may be greater than 0.000% and less than or equal to 0.400%.

[0047] Co is a component that reduces the coefficient of thermal expansion in Invar alloys when added at 4% or less, and increases the coefficient of thermal expansion when added above that amount. In this invention, through an evaluation of various component contents, a 3.00 x 10⁻³ material applicable as a material for liquefied natural gas storage containers is derived by considering the Co content along with the Cr and Ni contents. -6Conditions having a coefficient of thermal expansion of / ℃ or less were derived. In the present invention, the Co content can be limited to greater than 0.000% and less than or equal to 0.400%. Preferably, the Co content can be greater than or equal to 0.072% and less than or equal to 0.310%.

[0048] The remaining component of the present invention is iron (Fe). However, since unintended impurities from raw materials or the surrounding environment may inevitably be incorporated during the ordinary manufacturing process, they cannot be excluded. As these impurities are known to any person skilled in the ordinary manufacturing process, all details thereof are not specifically mentioned in this specification.

[0049] In addition, in addition to limiting the content of each alloying element to the conditions described above, the relationship between them can be further limited as follows.

[0050] The low thermal expansion steel of the present invention may have a value of the following formula (1) of 0.00 or more and 4.00 or less.

[0051] Equation (1): 0.5*[Cr] - [Ni] - 2.7*[Mn] - 4*[Co] + 40

[0052] (In the above formula (1), [Cr], [Ni], [Mn] and [Co] represent the content (weight%) of each element.)

[0053] The disclosed invention aims to suppress thermal expansion by lowering the coefficient of thermal expansion through the optimization of alloy components. Accordingly, the disclosed invention derived Equation (1) by combining alloy components that can affect the coefficient of thermal expansion. When the value of Equation (1) exceeds 4.00 or is less than 0.00, the coefficient of thermal expansion from room temperature to 100°C is 3.00 x 10 -6 It may exceed / ℃. Also, if the value of Equation (1) exceeds 4.00 or is less than 0.00, the coefficient of thermal expansion from 180℃ to 0℃ is 3.00 x 10 -6It may exceed / ℃. That is, if the value of Equation (1) exceeds 4.00 or is less than 0.00, the thermal expansion inhibition power may be inferior.

[0054] Within the range where the value of Equation (1) is 0.00 or higher and 4.00 or lower, the low thermal expansion steel according to one embodiment of the present invention has a low thermal expansion coefficient value and thus has less volume change with temperature change. Specifically, the value of Equation (1) may be 0.04 to 3.86.

[0055] In one embodiment, the low thermal expansion steel may have a value of the following formula (2) of 0.00 or less.

[0056] Equation (2): 175*[C] + 11[Si] + 3*[Mn] + 3*[Cr] - 8

[0057] (In Equation (2), [C], [Si], [Mn], and [Cr] represent the content (weight%) of each element.)

[0058] Within the range where the value of Equation (2) is 0.00 or less, the low thermal expansion steel according to one embodiment of the present invention may have a hardness of 200 Hv or less.

[0059] A low thermal expansion steel according to one embodiment has a coefficient of thermal expansion of 3.00 x 10⁻⁶ from room temperature to 100°C. -6 It may be below / ℃.

[0060] A low thermal expansion steel according to one embodiment has a coefficient of thermal expansion of 3.00 x 10 from -180°C to 0°C. -6 It can be below / ℃. Therefore, it can be applied as a material for liquefied natural gas storage containers.

[0061] A low thermal expansion steel according to one embodiment may have a hardness of 200 Hv or less. Due to the low hardness, machinability is improved and excellent crack resistance may be achieved.

[0062] A method for manufacturing low thermal expansion steel according to an example of the present invention comprises the steps of: manufacturing a steel material having, in weight %, C: greater than 0.000% and less than or equal to 0.040%, Si: greater than 0.080% and less than or equal to 0.200%, Mn: greater than 0.150% and less than or equal to 0.450%, P: greater than 0.000% and less than or equal to 0.0030%, S: greater than 0.0000% and less than or equal to 0.0030%, Cr: greater than 0.00% and less than or equal to 2.00%, Ni: greater than 34.0% and less than or equal to 39.0%, Co: greater than 0.000% and less than or equal to 0.400%, and the remainder being Fe and unavoidable impurities, wherein the value of the following formula (1) is 0.00 and less than or equal to 4.00; and reheating the steel material at a temperature of 1150℃ to 1300℃ and hot rolling it. The method includes the step of hot rolling annealing the above hot-rolled material at a temperature of 800°C to 1000°C.

[0063] Equation (1): 0.5*[Cr] - [Ni] - 2.7*[Mn] - 4*[Co] + 40

[0064] (In Equation (1), [Cr], [Ni], [Mn] and [Co] represent the content (weight%) of each element.)

[0065] In addition, the above steel material may have a value of 0.00 or less in the following formula (2).

[0066] Equation (2): 175*[C] + 11[Si] + 3*[Mn] + 3*[Cr] - 8

[0067] (In Equation (2), [C], [Si], [Mn], and [Cr] represent the content (weight%) of each element.)

[0068] To manufacture low thermal expansion steel according to the present invention, a steel material is first manufactured by continuous casting from molten steel having the compositional system of the present invention, and the explanation regarding the alloying element content and the reason for the numerical limitation of Equation (1) is as described above.

[0069] First, the steel can be reheated at 1150°C to 1300°C to decompose coarse precipitates generated during casting and to homogenize the internal structure. Subsequently, the reheated steel is hot-rolled to obtain a hot-rolled material. At this time, any hot-rolling process that is conventionally known can be applied without limitation to the present invention.

[0070] Next, hot-rolled steel sheets can be manufactured by hot-rolling annealing at 800°C to 1000°C. If the hot-rolling annealing temperature is low, segregation generated during casting may remain, resulting in inferior elongation. However, if the hot-rolling annealing temperature is excessively high, strength may decrease due to grain coarsening.

[0071] Next, if necessary, the method may further include the step of cold rolling the hot-rolled steel sheet with a reduction rate of 50% or more and cold rolling annealing at 800°C to 950°C to produce a cold-rolled steel sheet.

[0072] If the reduction rate is less than 50%, recrystallization is reduced during the rolling and annealing stage, which may result in coarsened grains. Therefore, in the present invention, it is preferable to control the reduction rate to 50% or more.

[0073] If the cold rolling annealing temperature is lower than 800°C, recrystallization may not be sufficient, resulting in a lower elongation. However, if the cold rolling annealing temperature is excessively high above 950°C, the grains become coarsened and the depth of oxides formed at the grain boundaries increases, which may lead to a deterioration in surface quality after pickling. Considering this, the cold rolling annealing temperature can be controlled to between 800°C and 950°C.

[0074] Although exemplary embodiments of the present invention have been described above, the present invention is not limited thereto, and those skilled in the art will understand that various changes and modifications are possible within the scope and concept of the claims set forth below.

[0075] {Example}

[0076] Slabs were manufactured in a vacuum induction melting furnace for various alloy composition ranges shown in Table 1 below. The manufactured slabs were reheated at 1200°C, hot-rolled at 1250°C, and hot-rolled annealed at 800°C to produce hot-rolled steel sheets.

[0077] Also, the values ​​of Equation (1) and Equation (2) are shown in Table 1 below. The value of Equation (1) was calculated using Equation (1) below.

[0078] Equation (1): 0.5*[Cr] - [Ni] - 2.7*[Mn] - 4*[Co] + 40

[0079] In the above equation (1), [Cr], [Ni], [Mn] and [Co] represent the content (weight%) of each element.

[0080] The value of Equation (2) was calculated using Equation (2) below.

[0081] Equation (2): 175*[C] + 11[Si] + 3*[Mn] + 3*[Cr] - 8

[0082] In the above equation (2), [C], [Si], [Mn] and [Cr] represent the content (weight%) of each element.

[0083] CSiMnPSCrNiCo Formula (1) Formula (2) Example 1 0.01 00.16 00.38 00.001 20.0005 1.023 7.5 0.07 21.70 -0.29 Example 20.009 0.15 00.43 00.001 00.0004 1.0039 00.07 40.04 -0.49 Example 30.022 0.14 00.28 00.0017 0.0008 0.49 36.20.11 02.85 -0.30 Example 40.018 0.18 00.19 00.0013 0.0005 0.1036.10.28 02.32 -2.00 Example 50.0200.1700.3900.00180.00120.4234.10.3003.86-0.20 Example 60.0160.1700.4100.00140.00110.1135.40.2902.39-1.77 Example 70.0080.0800.2800.00140.00200.0335.90.3102.12-4.79 Comparative Example 10.0270.2000.4200.00150.00220.4332.50.0426.411.48 Comparative Example 20.0100.1600.3700.00300.00190.0742.00.026-3.07-3.17 Comparative Example 30.0320.0900.6400.00310.00080.0438.20.230-0.830.63 Comparative Example 40.0160.1300.2200.00140.00041.6035.60.0974.221.69 Comparative Example 50.0270.0900.2900.00230.00040.9736.20.0563.281.50 Comparative Example 60.0310.1100.4100.00140.00052.0036.00.0313.775.87 Comparative Example 70.0310.2000.2400.00100.00050.1137.00.3171.140.68

[0084] In addition, Table 2 below shows the coefficient of thermal expansion from room temperature to 100°C, the coefficient of thermal expansion from -180°C to 0°C, and the hardness. The coefficient of thermal expansion in the temperature range from room temperature to 100°C was measured using a dilatometer. A rod-shaped specimen with a diameter of 3 mm and a length of 10 mm was used. First, the change in length of the specimen according to the temperature change was measured while increasing the temperature from room temperature to 120°C at a rate of 1°C / s. Next, the linear coefficient of thermal expansion under conditions from 25°C to 100°C was calculated using the following equation (3).

[0085] Equation (3):

[0086] In Equation (3), α m L is the coefficient of thermal expansion, L0 is the initial length, △L is the change in length, and △T is the change in temperature.

[0087] The coefficient of thermal expansion in the temperature range from -180°C to 0°C was evaluated using a dilatometer capable of measurement by cooling with liquid helium. A rod-shaped specimen with a diameter of 9 mm and a length of 20 mm was used. After cooling and stabilizing to below -180°C using liquid helium, the change in length of the specimen was measured while increasing the temperature from 180°C to 0°C at a rate of 10°C / min. Next, the coefficient of linear expansion from -180°C to 0°C was also calculated according to the above equation (3).

[0088] In addition, the hardness of the steel was expressed as the average value measured 10 times with a 1kg load using a micro-Vickers hardness tester.

[0089] Thermal expansion coefficient from room temperature to 100°C (x10 -6 / ℃)-180℃~0℃ Thermal expansion coefficient(x10 -6 / °C) Hardness (Hv) Example 1 2.40 2.48 200 Example 2 2.87 2.8 2200 Example 3 1.85 2.14 200 Example 4 1.55 2.05 198 Example 5 2.57 1.15 200 Example 6 1.50 1.20 199 Example 7 1.17 1.37 196 Comparative Example 15.35 2.35 202 Comparative Example 25.10 7.00 197 Comparative Example 37.21 3.74 201 Comparative Example 43.18 4.01 202 Comparative Example 52.07 2.26 202 Comparative Example 62.92 2.53 206 Comparative Example 71.87 1.24 201

[0090] Referring to Table 1, Examples 1 to 7 satisfied the alloy composition, the value of Equation (1), and the value of Equation (2) presented in the disclosed invention. Therefore, referring to Table 2, for Examples 1 to 7, the coefficient of thermal expansion from room temperature to 100°C was 3.00 x 10⁻⁶. -6 / ℃ or less, coefficient of thermal expansion from -180℃ to 0℃ 3.00 x 10⁻⁶ -6 The conditions of / °C or less and hardness of 200 Hv or less were satisfied. That is, Examples 1 to 7 had low thermal expansion and low hardness. In the case of Comparative Example 1 and Comparative Examples 3 to 4, neither the range of values ​​of Equation (1) disclosed in the present invention nor the range of values ​​of Equation (2) were satisfied. Therefore, the coefficient of thermal expansion from room temperature to 100°C and / or from -180°C to 0°C was 3.00 x 10⁻⁶ -6 Thermal expansion occurred relatively significantly when exceeding / ℃. In addition, hardness was found to be relatively high when exceeding 200Hv.

[0091] In the case of Comparative Example 2, the value of Equation (1) is less than 0, falling outside the scope of the present invention, so the coefficients of thermal expansion from room temperature to 100°C and from -180°C to 0°C are both 3.00 x 10 -6 Thermal expansion occurred relatively significantly when exceeding / ℃. Meanwhile, the value of Equation (2) is controlled to be 0.00 or less, and it can be confirmed that a low hardness of 200 Hv or less is obtained.

[0092] Referring to Table 1, in the case of Comparative Examples 5 to 7, the range of values ​​for Equation (1) was satisfied, but the range of values ​​for Equation (2) was not satisfied. As a result, referring to Table 2, since the range of values ​​for Equation (1) is satisfied, the coefficients of thermal expansion from room temperature to 100°C and from -180°C to 0°C are all 3.00 x 10⁻⁶. -6 Thermal expansion occurred less than / ℃. However, as the range of values ​​in Equation (2) was not satisfied, the hardness was found to be higher than 200 Hv.

Claims

1. In weight %, C: greater than 0.000% and less than or equal to 0.040%, Si: greater than 0.080% and less than or equal to 0.200%, Mn: greater than 0.150% and less than or equal to 0.450%, P: greater than 0.000% and less than or equal to 0.0030%, S: greater than 0.0000% and less than or equal to 0.0030%, Cr: greater than 0.00% and less than or equal to 2.00%, Ni: greater than 34.0% and less than or equal to 39.0%, Co: greater than 0.000% and less than or equal to 0.400%, and the remainder comprises Fe and unavoidable impurities, Low thermal expansion steel having a value of the following formula (1) of 0.00 or more and 4.00 or less: Equation (1): 0.5*[Cr] - [Ni] - 2.7*[Mn] - 4*[Co] + 40 (In Equation (1), [Cr], [Ni], [Mn] and [Co] represent the content (weight%) of each element.) 2. In Claim 1, Low thermal expansion steel having a value of 0.00 or less in the following formula (2): Equation (2): 175*[C] + 11[Si] + 3*[Mn] + 3*[Cr] - 8 (In Equation (2), [C], [Si], [Mn] and [Cr] represent the content (weight%) of each element.) 3. In Claim 1, The coefficient of thermal expansion from room temperature to 100°C is 3.00 x 10 -6 Low thermal expansion steel with a temperature of / ℃ or less.

4. In Claim 1, The coefficient of thermal expansion from -180℃ to 0℃ is 3.00 x 10 -6 Low thermal expansion steel with a temperature of / ℃ or less.

5. In Claim 2, Low thermal expansion steel with a hardness of 200 Hv or less.

6. A step of manufacturing a steel material in weight %, wherein C: greater than 0.000% and less than or equal to 0.040%, Si: greater than 0.080% and less than or equal to 0.200%, Mn: greater than 0.150% and less than or equal to 0.450%, P: greater than 0.000% and less than or equal to 0.0030%, S: greater than 0.0000% and less than or equal to 0.0030%, Cr: greater than 0.00% and less than or equal to 2.00%, Ni: greater than 34.0% and less than or equal to 39.0%, Co: greater than 0.000% and less than or equal to 0.400%, and the remainder being Fe and unavoidable impurities, wherein the value of the following formula (1) is greater than or equal to 0.00 and less than or equal to 4.00; A step of reheating the above steel at 1150℃ to 1300℃ and hot rolling; A method for manufacturing low thermal expansion steel comprising the step of hot rolling annealing the above hot-rolled material at 800℃ to 1000℃: Equation (1): 0.5*[Cr] - [Ni] - 2.7*[Mn] - 4*[Co] + 40 (In Equation (1), [Cr], [Ni], [Mn] and [Co] represent the content (weight%) of each element.) 7. In Claim 6, The above steel material is, A method for manufacturing low thermal expansion steel in which the value of the following formula (2) is 0.00 or less: Equation (2): 175*[C] + 11[Si] + 3*[Mn] + 3*[Cr] - 8 (In Equation (2), [C], [Si], [Mn] and [Cr] represent the content (weight%) of each element.) 8. In Claim 6, A method for manufacturing low thermal expansion steel, further comprising the step of cold rolling the hot-rolled steel sheet with a reduction rate of 50% or more and cold rolling annealing at 800℃ to 950℃ to manufacture a cold-rolled steel sheet.

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